Heretofore, a fluorinated polymer excellent in heat resistance, chemical resistance, etc. has been used in various applications. In a fluorinated polymer, unstable terminal groups having a polymerization initiator, chain transfer agent, etc. bonded at terminals of the polymer, are present, whereby due to decomposition of such unstable terminal groups, the apparatus is likely to be corroded, or the fluorinated polymer itself is likely to be colored, at the time of molding the fluorinated polymer or during its use at a high temperature. As it contains such unstable terminal groups, the fluorinated polymer is likely to lose the ultraviolet light resistance, chemical resistance, optical properties, etc. which are otherwise intrinsic to the fluorinated polymer.
In order to solve such problems, a method is known to fluorinate a fluorinated polymer obtained by polymerization, in the presence of fluorine gas, to convert unstable terminal groups to perfluoromethyl groups (—CF3) (Patent Document 1).